To some degree, all eyes deviate from a perfect optical system. These deviations, or aberrations, include imperfections, irregularities, or distortions of the optical quality of the eye, and can lead to refractive or visual errors. Aberrations can be classified into low order and high order aberrations, and can be described mathematically, for example, by Zernike polynomials.
Low order aberrations include prismatic, spherical, and cylindrical errors. First order, or prismatic, errors include vertical prism and horizontal prism errors. Second order, or defocus and astigmatism, errors include myopia, hyperopia, 45/135 astigmatism, and 90/180 astigmatism, for example. Traditional forms of optical correction involve measuring low order aberrations and prescribing sphero-cylindrical lenses in the form of glasses, contact lenses, and refractive surgery.
High order aberrations, on the other hand, are aberrations of the optical system that go beyond nearsightedness, farsightedness, and astigmatism. For example, third order aberrations include trefoil and coma. Fourth order aberrations include Z(4,−4), Z(4,−2), spherical aberration, Z(4,2), and Z(4,4) errors. Generally, high order aberrations include third order errors and above. Such aberrations are typically not corrected with glasses or contact lenses. High order optical errors of the human eye can be responsible for reduced visual acuity in spite of an optimal spherical or cylindrical refraction.
Wavefront-guided refractive surgery provides one method for measuring and treating low order and high order optical distortions in the eye. Wavefront systems measure how light is distorted as it passes into the eye and then is reflected back. An optical map of the eye can be created, detailing specific imperfections. There are several ways of analyzing the optical system of the eye using wavefront technology. One of the more common approaches involves the Hartmann-Shack wavefront sensing method.
Refractive surgery, including wavefront-guided custom ablation treatment, is effective in laser vision correction. However, current systems and methods may be less than ideal, and may even introduce or amplify high order aberrations. In light of the above, it would be desirable to have improved methods, devices, and systems that reduce optical aberrations or inhibit refractive surgery induced aberrations. Relatedly, it would be desirable to have improved methods, devices, and systems that determine, predict, or otherwise characterize optical aberrations or refractive surgery induced aberrations.